1. Field of the Invention
The present invention relates to a bone implant member for bone, joint, as well as dental prostheses, bone connecting elements such as bone screws and splints, which consists of a mechanically stable carrier material compatible (biocompatible) with bone tissue and of bioactive calcium phosphate ceramic, in particular tri- and tetracalcium phosphate, as well as relating to a process for the production of such an implant member.
2. Discussion of the Prior Art
Presently known and most widely utilized implants consist of an anchoring component of metal which is to be inserted in the bone and are shaped in a form of a plate, needle, screw or the like, and are predicated on a purely mechanical intermeshing with the bone in order to attain an anchoring of the prosthesis on the bone. In the interim it has been recognized that numerous technical requirements must be concurrently fulfilled with respect to the material in order to achieve a durable stable implantation. The employed materials must be biocompatible with the bone and the shaping of the implants and the mechanical properties of the material must afford a biologically correct loading and introduction of forces since, otherwise, the bone will react through degeneration and, finally, through loosening of the implant. It has further been recognized that the implant must in all regions evidence a direct, durable, osseous-like connection with the bone and cannot be encapsulated relative to the bone through a connective tissue membrane.
For this purpose, bioactive materials have become known in more recent times which effect a connective tissueless growing together of the bone with the surface of the material of the anchoring component. With such materials this relates, for example, to calcium phosphates of predetermined composition wherein there takes place a direct connective tissueless growing together of the bone with the material (Koster, "Experimenteller Knochenersatz durch resorbierbare Calciumphosphatkeramik", Langenbecks Archiv fur Chirurgie 341, 77-86 (1976). These calcium phosphates are decomposable in the biological environment, in essence, they are absorbed by the cells which are active in the bone transformation, and thereby fulfill the predetermined basic biochemical condition, however, they do not come into consideration as a single material in a prosthesis which is permanently implanted due to a lack of an adequate inherent strength and due to a lack of a durable anchoring between the material of the anchoring component and the bone, because of the given reabsorbability.
In order to create a permanent anchoring for extensively loaded implants which will lead to a really permanent interconnection between the prosthesis and the tissue, it has become known from German-Laid Open Patent Application No. 26 20 907 that the anchoring of the prosthesis can be constructed as a prosthesis shaft coating from a plastic material which is mechanically and chemically stable in the environment of the body, and to so deposit therein ceramic calcium phosphate in a particulate form of predetermined particle size diameter so that there is produced a generally porous matrix of plastic material during the reabsorption of the ceramic components on whose inner pore surfaces there remain bioactivated residues of the ceramic.
In accordance with another proposal for an implantable tooth root as disclosed in German-Laid Open Patent Application No. 27 33 394, this essentially consists of a biostable polymer matrix which is compatible with human cell tissue, in which there are deposited the reabsorbable bioreactive calcium phosphate in a finely-dispersed form, which are encompassed by a thin, porous layer of nonreabsorbable calcium phosphate, and in which there is inserted a core as a connecting element for the mounting of a dental superstructure.
However, some hesitations exist in connection with the utilization of plastic materials in the form of a polymer matrix as a carrier member for the ceramic calcium phosphate although, at this time, they are still well employed in practice. Polymer plastics frequently also include monomers in other deleterious materials which in implants, after respective aging, can lead to exchange reactions with the tissue. Moreover, a plastic material carrier member does not allow for a sufficiently precise shaping and mechanical working in order to enable the construction of an implant equipped with a plastic material support member for the most different purposes, such as bone and joint protheses, or also for bone connecting elements, such as screws, splints and the like.